Cells, for example electrochemical cells, may be connected in series to form a battery. The cells may be damaged if upper and lower voltage limits of the cells are exceeded during charging and discharging of the battery. The voltages of the cells in the battery may be adjusted using active balancing. In top balancing, charge from a cell with a higher voltage than the other cells may be distributed to the battery. In bottom balancing, a cell with a lower voltage than the other cells may be charged by the battery. However, it may be difficult to determine the state of charge or state of health of individual cells in the battery, especially if the cells are connected in series.